Atrial fibrillation is a common sustained cardiac arrhythmia and a major cause of stroke. This condition is initiated by wavelets originating at or near the intersection of a generally cavernous region such as a pulmonary venous atrium or a pulmonary vein and a generally flat structure such as the left atrium. The condition is perpetuated by reentrant wavelets propagating in an abnormal atrial-tissue substrate. Various approaches have been developed to interrupt wavelets, including surgical or catheter-mediated atriotomy. A common procedure involves ablating a lesion to interrupt the wavelets using one or more electrodes mounted on the distal end of a generally-straight catheter. This procedure works well, for example, when ablating a line of block in the atria. In this case, the proximal portion and tip of the catheter are in contact with and supported/stabilized by the atria along the line of intended block. However, at the intersection of a generally cavernous or tubular region and a generally flat region in or around the heart, this procedure can be less effective. For example, when the line of block to be ablated is about the circumference of the cavernous or tubular region, the catheter is not stabilized or supported except at the tip where it contacts the heart making it is difficult to manipulate and control the distal end of a straight catheter for an effective ablation about the circumference. Catheters have been developed for ablating about an inner circumference of the tubular region, for example the pulmonary vein. For example, catheters using ultrasound transducers surrounded by an inflatable balloon have been used. The balloon in such a catheter is positioned inside the pulmonary vein. Balloons have also been used for stable placement inside the pulmonary vein, while ablating outside the pulmonary vein. However, due to the shape and material of the balloon, the balloon often becomes dislodged, thereby adversely affecting the accuracy of the lesion created outside the ostium of the pulmonary vein or pulmonary venous antrum. Moreover, due to the shape of regions near the pulmonary vein and/or the antrum of pulmonary veins, where a generally flat structure joins a generally cavernous structure, it is difficult to maintain a catheter in stable position. When the tip of the catheter approaches the intersection of a generally cavernous structure from the region of the generally flat structure the catheter section proximal the tip is not in contact with or supported/stabilized by the flat structure. Without supportive contact between this proximal catheter section and the tissue, motion of the heart during systole, diastole and respiration is not transmitted to this catheter section except by contact between tissue and the catheter tip. As the heart moves during systole, diastole and respiration, the contact pressure at the tip of the catheter may vary from excessive to nonexistent. In a catheter that approaches the intersection of the ostium and the atrium in a “forward” direction, the disparity between the generally motionless (or out of synch) catheter and the heart makes it difficult to maintain stable contact between the catheter tip and the intersection of the flat and cavernous regions in a beating moving heart. An unsupported and thus unsynchronized catheter used in these regions may be inadvertently advanced into the pulmonary vein or venous antrum. Also, the nonuniform contours at the intersection of the pulmonary vein or venous antrum and surrounding tissue can make it difficult to contact recessed areas without excess pressure on the protruding areas increasing the risk of perforation. In addition, the catheter position is maintained only by contact between the tip and the nonuniform contours causing the catheter tip to frequently lose contact with the tissue during ablation or mapping as the heart moves independently during systole, diastole and with respiration.
Accordingly, a need still exists for a catheter capable of effectively mapping and ablating regions at or near the intersection of the left atrium and the ostium of a pulmonary vein or venous antrum, where the catheter is better configured and adapted for use in such regions so as to contact the nonuniform tissue surface without undue force and maintain stability during ablation and mapping despite the motion of beating heart in a breathing patient. A catheter of such design improves precision of mapping and/or ablation and minimize risks of damage to the tissue, including tissue perforation and inadvertent entry into the pulmonary vein or pulmonary venous antrum causing stenosis of the cavernous structure.